Compressed gas operated engine

ABSTRACT

This engine is operated by compressed gas and comprises two cylinders with pistons therein, on piston rods that are pivoted to cranks fixed to a control shaft. This shaft carries a gear meshing with direction reversible gearing. The shaft also carries cams for operating valves that connect opposite ends of the cylinders to compressed gas supply and to vent. Means is provided to block off the compressed gas supply and vent to both ends of each cylinder and to interconnect both ends of each cylinder, to permit one cylinder to be under power while the piston in the other cylinder idles and is dragged by the piston in the powered cylinder. Both cylinders are never devoid of power at the same time.

United States Patent Stenger 1 Mar. 21, 1972 COMPRESSED GAS OPERATED ENGINE FOREIGN PATENTS OR APPLICATIONS 914,373 1/1963 Great Britain ..9l/188 Primary Examiner-Paul E. Maslousky Attorney.l. B. Felshin [57] ABSTRACT This engine is operated by compressed gas and comprises two cylinders with pistons therein, on piston rods that are pivoted to cranks fixed to a control shaft. This shaft carries a gear meshing with direction reversible gearing. The shaft also carries cams for operating valves that connect opposite ends of the cylinders to compressed gas supply and to vent. Means is provided to block off the compressed gas supply and vent to both ends of each cylinder and to interconnect both ends of each cylinder, to permit one cylinder to be under power while the piston in the other cylinder idles and is dragged by the piston in the powered cylinder. Both cylinders are never devoid of power at the same time. i

6 Claims, 10 Drawing Figures .ATENTEDMAR21 I972 SHEET 1 0F 4 INVENTOR. JOSiP/l 0. 379/652 '4 TTORNEY FIGI PATENTEDHARZI I972 SHEET 3 BF 4 INVENTOR. JOSEPH a. STE/V660 g6 Arron/vs? FIG.3

PAIENTEDMAR21 m2 3,650,179

sum u 0F 4 VAL VE 3A INVENTOR. JOJEPH OJTENGER COMPRESSED GAS OPERATED ENGINE This invention relates to compressed gas operated engines.

An object of this invention is to provide an engine of the character described which uses compressed air or nitrogen from tanks that pass to cylinders for moving piston rods carrying pistons disposed in the cylinders. The piston rods are pivoted to crank arms fixed to a control shaft which carries cams that operate valves which control passage of the compressed gases to the cylinders and connecting the cylinders to vent. This engine is of the type that can be mounted on a submersible cage carrying the gas tanks. The control shaft carries a gear meshing with reversing gearing to rotate a propeller or output shaft, in opposite directions, for moving the cage slowly through water.

Another object of this invention is to provide, in an engine of the character described, bypass conduit means to interconnect the ends of each of the cylinders, to permit one cylinder to idle while the other cylinder is under power and drags the piston of said one cylinder without appreciable resistance.

Yet another object of this invention is to provide in an engine of the character described, improved means for changing the direction of rotation of the propeller shaft.

A further object of this invention is to provide an engine of the character described having means to ensure that both cylinders are never without power at the same time.

Still another object of this invention is to provide a strong, rugged and durable engine of the character described which can operate while immersed in water, which shall be relatively inexpensive to manufacture, smooth and positive in operation, and practical and efficient to a high degree in use.

Other objects of this invention will in part be obvious and in part hereinafter pointed out.

The invention accordingly consists in the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter described, and of which the scope of invention will be indicated in the following claims. In the drawings:

FIG. 1 is a side elevational view of an engine embodying the invention;

FIG. 2 is a cross-sectional view taken on line 22 of FIG. 1;

FIGS. 3, 4, 5, and 6 are diagrammatic views showing the engine in four 90 angularly spaced positions;

FIG. 7a is a diagrammatic view of one of the four way valves in cam of "position;

FIG. 7b is a diagrammatic view of the cam of FIG. 7a in cam on" position;

FIG. 8a is a diagrammatic view of one of the three way valves in cam "off" position; and

FIG. 8b is a diagrammatic view of the valve of FIG. 8a in cam on" position.

Referring now in detail to the drawing, 10 designates an engine embodying the invention. Engine 10 comprises a supporting frame 11. Frame 11 comprises a pair of parallel, vertical tubes 12 (FIG. 1), and a pair of parallel, vertical tubes 13. The tubes 12 and 13 are equally spaced apart. Tubes 12 are aligned with tubes 13. Tubes 12 are interconnected at the top, by a horizontal tube 14. Tubes 13 are also interconnected at the top by a tube 14. Tubes 12 are interconnected by an intermediate tube 15. Tubes 13 are interconnected by an intermediate tube 16. Tubes 12 are interconnected to tubes 13 by top tubes 17. These tubes may be integrated and fixed by welding.

Welded to the undersides of tubes l4 are a pair of symmetrical angle shaped members 19 having top horizontal inwardly extending flanges 19a from the outer sides of which vertical flanges 19b extend downwardly. It is the flanges 190 which are welded to tubes 14. Said angle members 19 project outwardly beyond tubes 12, 13 as shown in FIG. I. Said members 19 are equally spaced from the central portions of tubes 14. Fixed to one end of flanges 19a of said members 19, is a bracket 20 centrally disposed between tubes 12 and 13, and projecting downwardly. Bracket 20 comprises a pair of parallel apertured ears 20a and carries a horizontal pivot bolt 21.

Fixed to the other ends of flanges 19a of said members 19, is a bracket 22 centrally disposed between tubes 12 and 13 and projecting downwardly. Bracket 22 comprises a pair of parallel apertured ears 22a and carries a horizontal pivot bolt 23 coaxial with bolt 21.

Pivoted to bolt 21 is one closed end of a cylinder 25. Slida- 1 ble in cylinder 25 is a piston 26 which is fixed to one end of piston rod 27 which slides out of a bushing at the opposite end of the cylinder. Pivoted to the outer end of piston rod 27 is one end of a crank arm 28.

Fixed to tubes 12 is a horizontal, angle shaped support 30. Fixed to the tubes 13 is a horizontal, angle shaped support 31 at the same level as support 30.

Supported on supports 30, 31 are aligned bearing blocks 32 joumaling a horizontal control shaft 33. The opposite end of crank arm 28 is fixed to one end of said shaft 33.

Pivoted to bolt 23 is one closed end of a second cylinder 35 in which a piston 36 slides. Fixed to piston 36 is a piston rod 37 projecting through a bushing in the lower end of cylinder 35. The lower end of piston rod 37 is pivoted to one end of a crank arm 38. The other end of crank arm 38 is fixed to the opposite end of said shaft 33.

Shaft 33 is rotated, in the manner hereinafter explained, in a counterclockwise direction, looking at FIG. 2. Crank arm 38 lags behind crank arm 28 as the shaft 33 is rotated in one direction.

Fixed on shaft 33 for rotation therewith are three parallel cams 40, 41 and 42. Carried by the middle of shaft 33, and fixed for rotation therewith is a gear 45.

Fixed to tubes 12 is a plate 46. Fixed to tubes 13 is a plate 47. Fixed to'plates 46 and 47 are opposed bearings 46a, 47a. Bearings 46a, 47a journal a transverse shaft 49 disposed below shaft 33 and parallel thereto. Fixed to shaft 49 is a central pinion 50. Pinion 50 is spaced below gear 45. Shaft 49 is in the same vertical plane with shaft 33. Bearings 46a, 47a also journal a transverse horizontal shaft 52 to which a pinion 53 is fixed. Pinion 53 meshes with gear 45.

Pivoted on shaft 49, and disposed on opposite sides of pinion 50, are a pair of brackets 54 joumaling a cross-shaft 55 Fixed on shaft 55 is a central pinion 56 meshing with gear 45 and pinion 50 in the position of said brackets 54 shown in FIG. 2. Shaft 49 is an output shaft. A propeller (not shown) may be fixed to shaft 49. When engine 10 is mounted on a submersible or water borne vessel, the propeller will move the engine and vessel.

Gear 45 moves in a counterclockwise direction, looking at FIG. 2. When the brackets 54 are in the position shown in FIG. 2, pinion 53 merely rotates but does not affect the output shaft. In such position of brackets 54, pinion 56 is rotated in a clockwise direction. Since it meshes with pinion 50, the output shaft is rotated in a counterclockwise direction (FIG. 2).

To reverse the direction of rotation of the output shaft, brackets 54 are rotated in a clockwise direction, looking at FIG. 2, to disengage pinion 56 from gear 45 and to mesh pinion 56 with pinion 53.

Fixed to tubes 12 is a plate 60 which carries a pair of similar, symmetrically disposed, three way valves 1, 1A set at an inclination of 45to the horizontal. Valves 1, 1A incline upwardly and inwardly.

Valve 1 has a valve stem 61. When said valve stem is out" as shown in FIG. 3, the valve is off cam and the valve connects a conduit connecting orifice 3 on said valve with a conduit connecting orifice 1 of said valve. In the position of FIG. 3, crank 28 is inclined 45 downwardly and to the left while crank 38 is inclined 45 downwardly and to the right. Looking at this figure, shaft 33 will rotate in a clockwise direction.

Cam 40 has two diametrically opposed uniform cam rise portions 40a and 40b of equal angular extent (76 effective cam angles). Valve 1A, in position of FIG. 3 also has its valve item out" and its conduit connection orifice 1 is in communication, through a valve passage 62, with a conduit connecting orifice 3. As shown in FIG. 3 conduit connection orifices 5 are not in communication with orifices 3 of valves 1 and 1A. The

outer ends of the valve stems 61 contact the low portions of the cam 40 and are located beyond opposite ends of the lower cam rise portion 40a. As shown in FIG. 3, the middle of cam rise portions 40a, 40b are in a vertical plane.

Valves 2 and 2A are similar to valves 1 and 1A, respectively and are inclined upwardly and inwardly at 45. Cam 41 is similar to cam 40 and similarly placed on shaft 33. Hence in FIG. 3, orifices l and 3 of valves 2 and 2A are in communication, and orifices 5 are not in communication with orifices 3. Cam 41 has cam rise portions 41a, 41b similar to cam rise portions 40a, 40b.

Cam 42 has one cam rise portion 65 of substantially 180 angular extent.

Valves 3 and 3A are similar and symmetrically disposed. These are four-way valves (FIGS. 7, 70). Each has a valve stem 66 and conduit connection orifices l and 5 which are in communication through valve passages 67, 68, respectively, with conduit connection orifices 2 and 3, respectively, when the valve stem is on the rise portion 65 of the cam (cam on position). In FIG. 3, cam rise portion 65 of cam 42 is to the left of a vertical plane passing through shaft 33. Valves 3 and 3A also are inclined at 45 upwardly and inwardly. Valve stem 66 of valve 3A is on the low part of the cam 42. In this position, conduit connection orifices 1 and 4 of valve 3A are in communication with orifices 3 and 2, respectively, of said valve, through valve passages 68, 67, respectively. Valves 2, 2A and 3, 3A are mounted on plate 60:: attached to tubes 13.

Cylinder 25 has a conduit connection orifice 250 at its upper end and an orifice 25b at its lower end. Cylinder 35 has a conduit connecting orifice 350 at its upper end and an orifice 35b at its lower end.

An inlet pipe 70 connected through a pressure reducing regulator to a compressed gas supply tank or cryogenic container with pressure building equipment (not shown), is connected to branch conduits 71 and 72. The tanks may supply air or nitrogen under pressure topipe 70. Conduit 72 is connected to orifice 1 of valve 3A. Orifice 3 of said valve 3A is connected by conduit 73 to orifice 1 of valve 1A. Orifice 3 of valve 1A is connected by conduit v74 to orifice 25b of cylinder 25. Orifice 25a of cylinder 25 is connected by conduit 75 to orifice 3 of valve 2A. Orifice l of valve 2A is connected by conduit 76 to orifice 2 of valve 3A. Orifice 4 of valve 3A is connected by conduit 77 to orifice 5 of valve 3A. Conduit 77 is connected by conduit 78 to a vent pipe 79. Orifice 5 of valve 2A connects to orifice 5 of valve 1A through a conduit 79a.

Branch conduit 71 connects to orifice 1 of valve 3. Orifice 2 of valve 3 connects to orifice 1 of valve 2 by means of conduit 80. Orifice 3 of valve 2 connects, through conduit 81, to orifice 35a of cylinder 35. Orifice 35b of cylinder 35 connects, through conduit 82, to orifice 3 of valve 1. Orifice l of valve 1 connects through conduit 83 to orifice 3 of valve 3. Orifice 5 of valve 3 connects through conduit 84 to orifice 4 of valve 3. Said conduit 84 connects through conduit 85 to said vent 79.

Orifice 5 of valve 2 connects to orifice 5 of valve 1, through conduit 86.

Conduits or pipes 74, 75, 81, 82 must be flexible to allow swinging of the cylinders 25, 35 about their hinges 21, 23, respectively. Conduits or pipes 70, 71, 72, 78, 85 and 79 could be flexible if desired. The remaining conduits could be rigid if desired.

In the FIG. 3 position, gas pressure supply from pipe 70 passes to conduit 72, orifice l of valve 3A, valve passage 68 of valve 3A, orifice 3 of valve 3A, conduit 73, orifice l of valve 1A, valve passage 62 of valve 1A, orifice 3 of valve 1A, conduit 74 to orifice 25b of cylinder 25, to move the piston rod 27 upwardly for swinging the crank 28 in a clockwise direction. Gas in cylinder 25 on opposite sides of the piston, moves out of orifice 25a of cylinder 25, through conduit 75 to orifice 3 of valve 2A, valve passage 62 of valve 2A, orifice l of valve 2A,

conduit 76, orifice 2 of valve 3, valve passage 67 of valve 3A,

orifice 4 of said valve 3A to conduits 77, 78 to the vent 79.

At the same time, compressed gas supply flows to conduit 71 to orifice l of valve 3, valve passage 67 of valve 3, orifice 2 35a of cylinder 35, to push the piston rod 37 down.

At this time, gas is being pushed from the opposite side of the piston in cylinder 35 out through orifice 35b, conduit 82, orifice 3 of valve 1, valve passage 62 of valve 1, orifice 1 of said valve 1, conduit 83, orifice 3 of valve 3, passage 68 of valve 3, orifice 5 of valve 3 and conduits 84, to vent 79.

At the moment of the FIG. 3 position, both cylinders are under power.

As the parts move from the position of FIG. 3 toward the position of FIG. 4, cylinder 25 remains under power but cylinder 35 loses power and the piston in said cylinder is dragged, through shaft 33 by power applied to cylinder 25.

As the shaft rotates past the position of FIG. 3, valves 1A, 2A, and 3A remain in off cam position so that power continues to flow to cylinder 25 on one side of the piston therein, while the other side of the piston is vented, all in the manner described above.

However, as the shaft 33 moves from the FIG. 3 position for 45, valve 3 remains in cam on position as shown in FIG. 3, but valves 1 and 2 move to cam on positions (see FIGS. 7b and 8b). In such position, compressed gas from pipe 70 is in conduit 71, valve passage 67 of valve 3, conduit 80, but is shut off or blocked at orifice l of valve 2, because in the cam "on position of valve 2, orifice l is closed. Thus, there is no pressure on the upper side of the piston in cylinder 35 during the 45 movement of cranks 28, 38 from their FIG. 3 position in the direction of rotation.

Also the opposite side of the piston of cylinder 35 is cut off from vent, because at this time, valve 1 is in cam on position municates with the lower side of the piston of said cylinder 35,

so that as the piston is moved, gas merely is shoved in one direction. During the 45 rotation from FIG. 1 position, orifice 35a of cylinder 35, communicates, through conduit 81, orifice 3 of valve 2, passage 62 of said valve 2, orifice 5 of saidvalve 2, conduit 86, orifice 5 of valve 1, valve passage 62 of valve 1, orifice 3 of valve 1 and conduit 82 to orifice 35b of said cylinder 35.

As the shaft 33 moves beyond 45 from the FIG. 3 position, cylinder 25 will remain under power because valves 1A, 2A and 3A remain in cam off position, to continue moving the piston rod of said cylinder upwardly.

During said next 45 of movement, valves 1 and 2 remain in cam on" position while valve 3 goes to'cam off" position. Cylinder 35 is cut off during this period both from gas pressure and vent. This is so, because orifice l of valve 1 is shut, and orifice 1 of valve 2 is shut. Orifices 35a and 35b nevertheless intercommunicate through valves 1 and 2. Thus, as the shaft 33 moves from the FIG. 3 to the FIG. 4 position, cylinder25 is powered to move its piston up and drag the piston of cylinder 35 down.

When the parts reach the FIG. 4 position, valves 1 and 2 move from cam on" position to cam off position causing compressed gas to startmoving the piston of cylinder 35 upwardly and connecting the cylinder, above the piston to vent.

As the parts move beyond the FIG. 4 position, valve 3A remains in cam off position for 45 while valves 1A and 2A move to cam on" position, thus shutting off cylinder 25 from I compressed gas and ventand interconnecting orifices 25a,

cam off position. Va'lve 3A changes from valve ofF to valve on" position, but the compressed gas is cut off at valve 2A and vent is cut off at valve 1.

During the movement from FIG. to FIG. 6, cylinder 25 remains powered to move its piston down while the piston of cylinder 35 is dragged through the next 90'.

It will be noted that at the end of each 90 rotation, both cylinders are powered, to prevent a situation where both cylinders are without power at any one movement. If at any one time, both cylinders were without power, there would be no way to move them to powered position except manually or by reason of inertia. If inertia fails and it is difficult to continue movement manually, the engine would stop.

The reason that both cylinders do not lose power at the same time, is because the cams 40a, 40b and 41a, 411; are less than 90 in angular extent. Angles of 76 for the high parts of the cams has proven practical to allow valve stems 61 of valves 1, 1A and 2, 2A to be in cam off position at the same time, as shown in FIG. 3, 4, 5 and 6, momentarily before either valves 1,2 (FIGS. 3 and 5) or valves 1A, 2A (FIGS. 4 and 6) change to cam on positions.

It will thus be seen that there is provided an article in which the several objects of this invention are achieved, and which is well adapted to meet the conditions of practical use.

As possible embodiments might be made of the above invention, and as various changes might be made in the embodiments above set forth, it is to be understood that all matter herein set forth or shown in the accompanying drawings, is to be interpreted as illustrative only. Short travel of the valve stems relativeto large diameters of the cams, together with relatively small cam rise causes a rapid transfer of compressed gas through the system, resulting in extreme efficient operation. This is because of the small angular extent of cam rotation required to actuate the valve stem in opposite directions.

With use of cams of 3 inch radius and one-eighth inch cam rise, it requires about 3% rotation of the cams to actuate the valves. Thus, with a cam of such diameter, a cam rise of 76 having ramps at its end of 7 each, making a total of 90, movement of the'stem about half way up or down each ramp will operate the valve, thus requiring about a 3% angular movement of the cam to effect operation of the valve. This arrangement results in quick valve operation. When the cams move at about one revolution per second, the valve actions require only about one-one hundreth of a second in period of time. This speed operates efficiently with pressures up to 100 lbs. per square inch. The period could be extended to onetwentieth of a second at reduced pressure of 20 pounds per square inch.

It will be observed that in the position of FIG. 3, the pressure above the piston of cylinder 35 is full pressure (being connected to supply pressure) whereas the pressure below the piston is zero (being open to vent). As the engine moves beyond the position of FIG. 3, toward the position of FIG. 4, valves 3 and 3A do not change. Valves 1 and 2 will begin to operate, thereby causing orifices 35a and 35b to be interconnected but to shut off from both supply pressure and vent. The air pressure then equalizes to both sides of the piston in cylinder 35, but becomes reduced due to expansion of the gas into the space below the piston which was at zero pressure.

When the position of FIG. 4 is reached, supply pressure goes to the cylinder 35, below the piston of said cylinder. Since this part of the cylinder was under partial pressure, it does not require change from zero to maximum pressure, thereby reducing the amount of gas under pressure required for operation, and reducing the number of gas tanks necessary for operating the engine.

What is claimed is:

1. An engine comprising a control shaft, a pair of pivoted cylinders, pistons in the cylinders, piston rods fixed to said pistons, crank arms pivoted to said piston rods and fixed to said control shaft, means to supply gas under compression, bent means, conduit means to connect opposite ends of said cylinders to said gas supply means and to said vent means, cam means controlle by rotation of said control shaft, and valve means controlled by said cam means and controlling said conduit means to control reciprocation of said pistons and rotation of said control shaft, said cam means and valve means including means to apply power to one of said cylinders during a first two separate angles of movement for each revolution of the control shaft, to cause its piston to drive said shaft during said two angles, and to power the other cylinder during a second two separate angles of movement for each revolution of said control shaft, alternating with the first two angles of movement, to cause its piston to drive said shaft during said second two angles of movement for each revolution of said shaft, and means to interconnect opposite ends of the other cylinder, and to block said opposite ends of said other cylinder from said gas supply means and from said vent means, during the first two angles of movement, and to interconnect the opposite ends of the first cylinder and to block and opposite ends of said first cylinder from said gas supply means and from said vent means, during said second two angles of movement, whereby when the piston of one cylinder is being power driven, the piston in the other cylinder is being dragged by the piston in the powered cylinder.

2. The combination of claim 1, and said cam means and valve means including means to ensure connection of one end of at least one of said cylinders with said fluid supply means and connection of the other end of said one of said cylinders with said vent during the entire revolution.

3. The combination of claim 2, said crank arms being spaced apart 4. The combination of claim 1, said cam means and valve means further including means to cause said interconnection of said opposite ends of said other cylinder and blocking of said'opposite ends of said other cylinder from said gas supply means and from said vent means, substantially simultaneously, and to cause said interconnection of the opposite ends of said first cylinder and to cause said blocking of said opposite ends of said first cylinder from said gas supply means and from said vent means, substantially simultaneously.

5. An engine comprising a control shaft, a pair of pivoted cylinders, pistons in the cylinders, piston rods fixed to said pistons, crank arms pivoted to said piston rods and fixed to said control shaft, means to supply gas under compression, vent means, conduit means to connect opposite ends of said cylinders to said gas supply means and to said vent means, cam means controlled by rotation of said control shaft, and valve means controlled by said cam means and controlling said conduit means to control reciprocation of said pistons and rotation of said control shaft, said cam means and valve means comprising means to connect said gas supply means to one end of a cylinder and concurrently connect the other end of said cylinder to said vent means, to thereafter interconnect both ends of said cylinder and block both ends from said gas supply means and from said vent means to equalize pressure on both sides of the piston of said cylinder, and to thereafter connect said other end of said cylinder to said gas supply means and concurrently connect the ends of said cylinder to said vent means.

6. The combination of claim 5, said cam means and valve means further comprising means to effect said interconnection of said opposite ends of said cylinder, and said blocking of said ends of said cylinder from said supply means and from said vent means, substantially simultaneously. 

1. An engine comprising a control shaft, a pair of pivoted cylinders, pistons in the cylinders, piston rods fixed to said pistons, crank arms pivoted to said piston rods and fixed to said control shaft, means to supply gas under compression, bent means, conduit means to connect opposite ends of said cylinders to said gas supply means and to said vent means, cam means controlled by rotation of said control shaft, and valve means controlled by said cam means and controlling said conduit means to control reciprocation of said pistons and rotation of said control shaft, said cam means and valve means including means to apply power to one of said cylinders during a first two separate angles of movement for each revolution of the control shaft, to cause its piston to drive said shaft during said two angles, and to power the other cylinder during a second two separate angles of movement for each revolution of said control shaft, alternating with the first two angles of movement, to cause its piston to drive said shaft during said second two angles of movement for each revolution of said shaft, and means to interconnect opposite ends of the other cylinder, and to block said opposite ends of said other cylinder from said gas supply means and from said vent means, during the first two angles of movement, and to interconnect the opposite ends of the first cylinder and to block and opposite ends of said first cylinder from said gas supply means and from said vent means, during said second two angles of movement, whereby when the piston of one cylinder is being power driven, the piston in the other cylinder is being dragged by the piston in the powered cylinder.
 2. The combination of claim 1, and said cam means and valve means including means to ensure connection of one end of at least one of said cylinders with said fluid supply means and connection of the other end of said one of said cylinders with said vent during the entire revolution.
 3. The combination of claim 2, said crank arms being spaced apart 90*.
 4. The combination of claim 1, said cam means and valve means further including means to cause said interconnection of said opposite ends of said other cylinder and blocking of said opposite ends of said other cylinder from said gas supply means and from said vent means, substantially simultaneously, and to cause said interconnection of the opposite ends of said first cylinder and to cause said blocking of said opposite ends of said first cylinder from said gas supply means and from said vent means, substantially simultaneously.
 5. An engine comprising a control shaft, a pair of pivoted cylinders, pistons in the cylinders, piston rods fixed to said pistons, crank arms pivoted to said piston rods and fixed to said control shaft, means to supply gas under compression, vent means, conduit means to connect opposite ends of said cylinders to said gas supply means and to said vent means, cam means controlled by rotation of said control shaft, and valve means controlled by said cam means and controlling said conduit means to control reciprocation of said pistons and rotation of said control shaft, said cam means and valve means comprising means to connect said gas supply means to one end of a cylinder and concurrently connect the other end of said cylinder to said vent means, to thereafter interconnect both ends of said cylinder and block both ends from said gas supply means and from said vent means to equalize pressure on both sides of the piston of said cylinder, and to thereafter connect said other end of said cylinder to said gas supply means and concurrently connect the ends of said cylinder to said vent means.
 6. The combination of claim 5, said cam means and valve means further comprising means to effect said interconnection of said opposite ends of said cylinder, and said blocking of said ends of said cylinder from said supply means and from said vent means, substantially simultaneously. 